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Voyager 1 and 2 are only the two spacecraft that have arrived and passed through the heliospheric boundaries. Based on the plasma data from the Voyager 2 spacecraft, the electron quasi-thermal noise (QTN) is investigated by using of the electron population model consisting of a core with Maxwellian distribution and a halo with kappa distribution. The power spectra of the electron QTN is calculated at different heliocentric distances from 1 to 110 au. The parametric dependence of the QTN power spectra and the effective Debye length on the model parameters, such as the density ratio and temperature ratio of the halo to the core, kappa index and the antenna length, are discussed further. The results show that the electron QTN spectrum consists of a plateau in the low frequency band f < f _pt , a prominent peak at the plasma frequency f _pt , and a rapid decreasing part in the high frequency band f > f _pt . The QTN plateau level basically falls down outwards until the termination shock crossing at about 84 au, after which the plateau rebounds a little near the heliopause. Although the model parameters can be very variable, the QTN plateau level does not present more than the double change in a fairly wide range of the model parameters. The presented results can be useful for future deep-space explorations in the heliosphere and can provide valuable references for the design of onboard detectors.

To evaluate the effect of surface reaction process after hydrofluoric (HF) acid etching using ultrasound and the shear bond strength (SBS) of resin cement to zirconia polycrystal (Y-TZP) ceramic. Y-TZP ceramic sheets were divided into rinsing group (Group P), ultrasonic cleaning group (Group C), and ultrasonic reaction + rinsing group (Group CP), and all the groups were treated for 5, 10, 20, 30, 40, 50, and 60 min, respectively. The surface morphology, elements distribution, roughness, and wettability of the ceramic sheets in each group were observed. The SBS of ceramic-resin bonding specimens was tested after immersion and after cooling-heating cycles, respectively. Octahedral and spiculate products were observed on the surface of Y-TZP that was etched with HF acid in Group P. The amount of these products increased over time. In contrast, only a few octahedral products remained on the surface of Y-TZP in Groups C and CP. Within the same reaction time, the surface reaction of the CP group was stronger than that of the other two groups, accompanied by a more uniform morphology. The shear force in Group C was the lowest, and the shear force reduction in Group CP was the least after cooling-heating cycling, with statistically significant differences (P< 0.05). After the reaction time exceeded 30 min, the shear force in each group decreased instead of increasing. Octahedral and spiculate acid etching products on the surface of HF acid-etched Y-TZP can enhance the bonding force of zirconia. Ultrasonic cleaning would drive the exfoliation of acid etching products from the sample surface, leading to the decrease of the bonding force. The acid etching with ultrasonic vibration can accelerate the HF acid etching process of Y-TZP ceramics, which is conducive to improving the bond strength to resin and durability.

In this study, we conducted molecular dynamic simulations to investigate the thermal expansion behavior of Janus MoSSe nanotubes. We focused on understanding how the intrinsic strain in these nanotubes affects their thermal expansion coefficient (TEC). Interestingly, we found that Janus MoSSe nanotubes with sulfur (S) on the outer surface (MoSeS) exhibit a different intrinsic strain compared to those with selenium (Se) on the outer surface (MoSSe). In light of this observation, we explored the influence of this intrinsic strain on the TEC of the nanotubes. Our results revealed distinct trends for the TEC along the radial direction (TEC- r) and the axial direction (TEC- l x ) of the MoSSe and MoSeS nanotubes. The TEC- r of MoSeS nanotubes was found to be significantly greater than that of MoSSe nanotubes. Moreover, the TEC- l x of MoSeS nanotubes was smaller than that of MoSSe nanotubes. Further analysis showed that the TEC- r of MoSeS nanotubes decreased by up to 37% as the radius increased, while that of MoSSe nanotubes exhibited a slight increase with increasing radius. On the other hand, the TEC- l x of MoSeS nanotubes increased by as much as 45% with increasing radius, whereas that of MoSSe nanotubes decreased gradually. These opposite tendencies of the TECs with respect to the radius were attributed to the presence of intrinsic strain within the nanotubes. The intrinsic strain was found to play a crucial role in inducing thermally induced bending and elliptization of the nanotubes' cross-section. These effects are considered key mechanisms through which intrinsic strain influences the TEC. Overall, our study provides valuable insights into the thermal stability of Janus nanotubes. By understanding the relationship between intrinsic strain and the thermal expansion behavior of nanotubes, we contribute to the broader understanding of these materials and their potential applications. [ABSTRACT FROM AUTHOR]

This paper proposes a Whipple structure to enhance the impact resistance of graphene/aluminum alloy composites by varying the interlayer spacing between graphene and aluminum alloy. The increased interlayer spacing provides more deformation space for the graphene to absorb more deformation energy, and enables the formation of a debris cloud from the bullet fragments and graphene fragments, significantly reducing the impact energy per unit area of the next material. The impact limit serves as a critical metric for assessing the impact resistance of the Whipple structure. Based on molecular dynamics simulations, we developed a machine learning model to predict the protection of aluminum alloy, and quickly determined the impact limits of velocity, bullet radius, and interlayer spacing by using the machine learning model. An empirical equation for the impact limit of interlayer spacing was established. The results showed that non-zero interlayer spacing can significantly improve the impact resistance of the hybrid structure; to fully exploit the superior impact resistance of this Whipple structure, the number of graphene layers should be at least 3. Furthermore, at high impact velocities and large bullet radii, the impact limit of the interlayer spacing exhibits a substantial correlation with the number of graphene layers. These results provide valuable information for the design of the impact resistance of the graphene/aluminum alloy composites. [ABSTRACT FROM AUTHOR]

Thermal conductivity of porous graphene can be affected by defect concentration, nanopore shape and distribution, and it is hard to clarify the effects due to the correlation of those factors. In this work, molecular dynamics simulation is used to compare the thermal conductivity of graphene with three shapes of regularly arranged nanopores. The results prove the dominant role of defect concentration under certain circumstances in reducing thermal conductivity, while the coupling effect of nanopore shape should be noticed. When the atoms at the local phonon scattering area around each nanopore are properly removed, the abnormal increment of thermal conductivity can be detected with the increase of defect concentration. Heat flux vector angles can effectively characterize the local phonon scattering area, which can be used to describe the effect of nanopore shape. The coupling effect of defect concentration and pore shape with similar heat flux path is clarified according to this process. By adjusting vertex angle of triangle defect, there is a balanced state of the effect factors between the variation of defect concentration and the same phonon scattering area. It provides a possible way to describe the weighing factors of the coupling effect. The results suggest a feasible approach to optimize and regulate thermal properties of porous graphene in nanodevice. [ABSTRACT FROM AUTHOR]

Few-layer graphene has been widely regarded as an efficient filter for gas separation, but the effect of the layer number on the gas permeation process is still unclear. To explore the layer number effect, we perform molecular dynamics simulations to investigate the gas permeation through a nanopore within the few-layer graphene. Our numerical simulations show that the permeation constant decreases with increasing layer number, which is analyzed based on the macroscopic Kennard empirical model. The macroscopic model is in good agreement with the numerical result in the limit of large layer number, but there are obvious deviations for the medium layer number. We generalize the macroscopic model by considering the nanoscale effect from the surface morphology of the nanoscale pore, which can well describe the layer number dependence for the gas permeation constant in the full range. These results provide valuable information for the application of few-layer graphene in the gas permeation field. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures inherit many novel electronic and optical properties from their constituent atomic layers. Mechanical stability is key for realizing high-performance nanodevices based on van der Waals heterostructures. However, buckling instability is a critical mechanical issue for heterostructures associated with its two-dimensional nature. Using molecular dynamics simulations of graphene/MoS2 heterostructures, we demonstrate the relationship between buckling instability and the misfit strain that arises inevitably in such heterostructures. The impact of misfit strain on buckling depends on its magnitude: (1) A negative misfit strain causes a pre-compression of the graphene layer, which in turn initiates and accelerates buckling in this layer and reduces the buckling stability in the heterostructure as a whole. (2) A small positive misfit strain enhances the buckling stability of the graphene/MoS2 heterostructure by pre-stretching and hence decelerating the buckling of the graphene layer (where heterostructure buckling is initiated). (3) In the case of a large positive misfit strain, the graphene layer is pre-stretched while the MoS2 layer is significantly pre-compressed, so that heterostructure buckling is initiated by the MoS2 layer. Consequently, the buckling stability of the graphene/MoS2 heterostructure is reduced by increasing the large positive misfit strain. These findings are valuable for understanding the mechanical properties of van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

The thermal expansion effect plays an important role in governing the thermal stability or the stable configuration of quasi-two-dimensional atomic layers, where the difference between the thermal expansion coefficient of different kinds of atomic layer in lateral heterostructure may cause strong thermal rippling of the atomic layer. We investigate the thermal expansion phenomenon in the WSe2–MoS2 lateral heterostructure. We find that the thermal expansion coefficient can be enhanced by more than a factor of two via varying the ratio between the WSe2 and MoS2 components in the heterostructure. The underlying mechanism is disclosed to be the buckling of the WSe2 region that is induced by the misfit strain at the coherent interface between WSe2 and MoS2. These findings shall be helpful in handling the thermal stability of functional devices based on the transition-metal dichalcogenide lateral heterostructures and other similar quasi-two-dimensional lateral heterostructures. [ABSTRACT FROM AUTHOR]

The continuous loading assumption is adopted in most present studies on the buckling of thin shells subjected to lateral loads, while the relationship between the finite number of loads and the lateral buckling remains unclear. In this work, we derive an analytic formula for the dependence of the critical buckling stress on the number of loads, which shows that the critical stress increases significantly with the increase of the load number and reaches a saturation value in the limit of large load number. Furthermore, the analytic formula reveals the dependence of the critical stress on the deviation of the radius in an imperfect shell. To verify the validity of the analytic formula, we perform molecular dynamics simulations to investigate the buckling of both perfect and imperfect single-walled carbon nanotubes under a finite number of lateral loads, where the analytic formula agrees with the simulation results. These results shall be valuable for understanding mechanical stability of elastic thin shells or nanoscale tubal structures subjected to discrete lateral loads. [ABSTRACT FROM AUTHOR]

The cross-sectional shape of the nanotube is a key factor governing fundamental mechanical properties of the nanotube and the nanotube forest. In contrast to most circular nanotubes, in the present work, we demonstrate that the holey phenine nanotubes have polygonal cross sections with diameter-dependent number of sides. The non-circular cross section is attributed to the high twistability of the continuous C–C chains in the phenine nanotube. Consequently, the phenine nanotube forest has a square lattice structure rather than the regular hexagonal lattice of the carbon nanotube forest, resulting in a smooth buckling process under biaxial compression. The buckling pattern of the phenine nanotube forest is highly ordered with the orientation determined by the initial dislocation that frequently appears in the phenine nanotube forest. [ABSTRACT FROM AUTHOR]

We study the phonon modes in single-walled MoS2 nanotubes via lattice dynamics calculation and molecular dynamics simulation. The phonon spectra for tubes of arbitrary chiralities are calculated from a dynamical matrix constructed by the combination of an empirical potential with the conserved helical quantum numbers (κ, n). In particular, we show that the frequency (ω) of the radial breathing mode is inversely proportional to the tube diameter (d) as ω = 665.3/d cm−1. The eigenvectors of the twenty lowest-frequency phonon modes are illustrated. Based on these eigenvectors, we demonstrate that the radial breathing oscillation is initially disturbed by phonon modes of three-fold symmetry, then eventually the tube is squashed by modes of two-fold symmetry . Our study provides fundamental knowledge for further investigations of the thermal and mechanical properties of MoS2 nanotubes. [ABSTRACT FROM AUTHOR]

We perform classical molecular dynamics simulation to investigate the mechanisms underpinning the unresolved, experimentally observed temperature-dependent scaling transition in the quality factors of graphene nanomechanical resonators (GNMRs). Our simulations reveal that the mechanism underlying this temperature scaling phenomenon is the out-of-plane migration of adsorbates on GNMRs. Specifically, the migrating adsorbate undergoes frequent collisions with the GNMR, which strongly influences the resulting mechanical oscillation, and thus the quality factors. We also predict a discontinuous transition in the quality factor at a lower critical temperature, which results from the in-plane migration of the adsorbate. Overall, our work clearly demonstrates the strong effect of adsorbate migration on the quality factors of GNMRs. [ABSTRACT FROM AUTHOR]

We derive, from an empirical interaction potential, an analytic formula for the elastic bending modulus of single-layer MoS2 (SLMoS2). By using this approach, we do not need to define or estimate a thickness value for SLMoS2, which is important due to the substantial controversy in defining this value for two-dimensional or ultrathin nanostructures such as graphene and nanotubes. The obtained elastic bending modulus of 9.61 eV in SLMoS2 is significantly higher than the bending modulus of 1.4 eV in graphene, and is found to be within the range of values that are obtained using thin shell theory with experimentally obtained values for the elastic constants of SLMoS2. This increase in bending modulus as compared to monolayer graphene is attributed, through our analytic expression, to the finite thickness of SLMoS2. Specifically, while each monolayer of S atoms contributes 1.75 eV to the bending modulus, which is similar to the 1.4 eV bending modulus of monolayer graphene, the additional pairwise and angular interactions between out of plane Mo and S atoms contribute 5.84 eV to the bending modulus of SLMoS2. [ABSTRACT FROM AUTHOR]

We perform molecular dynamics simulations to investigate the effect of polar surfaces on the quality (Q)-factors of zinc oxide (ZnO) nanowire-based nanoresonators. We find that the Q-factors in ZnO nanoresonators with free polar (0001) surfaces are about one order of magnitude higher than in nanoresonators that have been stabilized with reduced charges on the polar (0001) surfaces. From normal mode analysis, we show that the higher Q-factor is due to a shell-like reconstruction that occurs for the free polar surfaces. This shell-like reconstruction suppresses twisting motion in the nanowires such that the mixing of other modes with the resonant mode of oscillation is minimized, and leads to substantially higher Q-factors in ZnO nanoresonators with free polar surfaces. [ABSTRACT FROM AUTHOR]

We perform both classical molecular dynamics simulations and beam model calculations to investigate the Young's modulus of kinked silicon nanowires (KSiNWs). The Young's modulus is found to be highly sensitive to the arm length of the kink and is essentially inversely proportional to the arm length. The mechanism underlying the size dependence is found to be the interplay between the kink angle potential and the arm length potential, where we obtain an analytic relationship between the Young's modulus and the arm length of the KSiNW. Our results provide insight into the application of this novel building block in nanomechanical devices. [ABSTRACT FROM AUTHOR]

The mechanical properties of supergraphene, cy clicgraphene and graphyne are studied using molecular dynamics simulations based on the AIREBO potential. In particular, we present the chirality-dependence of their mechanical properties, including Young's moduli, shear moduli, Poisson's ratios, ultimate strength and ultimate strains. The relationship of their Young moduli, shear moduli and Poisson ratios is in the order of Ysu (super) < Ycy (cy clic) < Ygy (graphyne) < Yge (graphene), Gsu < Gcy < Ggy < Gge and vsu > vcy > vgy > vge in corresponding zigzag and armchair sheets, respectively. Their intersheet adhesion energy is obtained as γsu D 30, γcy D 99 and γgy D 149 mJ m-2, which are much lower than that of γge D 291 mJ m-2 (the value is in good agreement with the latest experimental result γge D 310 ± J m-2). The obtained adhesion energy is accurately characterized by continuum modeling of the van der Waals interactions. Our study is very useful for the future applications of graphene-like materials in nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

Through a lattice dynamics analysis, it is revealed that the bubble plays a role of energy shield in the graphene, which helps to split the normal modes into two categories of distinct topological nature, namely the bright and dark modes. The topological invariants, Euler characteristic, of the bright and dark modes are 1 and 0, respectively. For bright modes, the energy is confined inside the bubble, so this type of modes is sensitive to the shape of the bubble; while the opposite phenomenon is observed for the dark modes. The different behavior of these two types of normal modes is examined and verified in the process of phonon thermal transport. The bright and dark modes are expected to be distinguished in experiment with existing scanning force microscope techniques, and they should play significant roles in many other physical processes. [ABSTRACT FROM AUTHOR]

Molecular-dynamics simulations are performed to study graphene-based torsional mechanical resonators. The quality factor is calculated by QF = ωτ/2π, where the frequency ω and lifetime τ are obtained from the correlation function of the normal mode coordinate. Our simulations reveal the radius dependence of the quality factor as QF = 2628/(22R-1 +0.004R2), which yields a maximum value at some proper radius R. This maximum point is due to the strong boundary effect in the torsional resonator, as disclosed by the temperature distribution in the resonator. Resulting from the same boundary effect, the quality factor shows a power law temperature dependence with power factors below 1.0. The theoretical results supply some valuable information for the manipulation of the quality factor in future experimental devices based on the torsional mechanical resonator. [ABSTRACT FROM AUTHOR]

Sn4P3 thin films have been successfully fabricated by reactive pulsed laser deposition for the first time and were investigated for their electrochemistry with lithium. The reversible discharge capacity of Sn4P3/Li cells cycled between 0 and 3.0 V was found to be about 906.2 mAh g-1. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, both the classical alloying process and the phosphorization/reduction of nanosized Sn were revealed in the lithium electrochemical reaction of Sn4P3 film electrode. Large reversible capacity of Sn4P3 made it a potential anode material for future lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The mechanism of the famous phase compression is discussed, and it is used to control the chaos in the Hindmarsh-Rose (H-R) model. It is numerically confirmed that the phase compression scheme can be understood as one kind of intermittent feedback scheme, which requires appropriate thresholds and feedback coefficient, and the intermittent feedback can be realized with the Heaviside function. In the case of control chaos, the output variable (usually the voltage or the membrane potential of the neuron) is sampled and compared with the external standard signal of the electric electrode. The error between the sampled variable and the external standard signal of the electrode is input into the system only when the sampled variable surpasses the selected thresholds. The numerical simulation results confirm that the chaotic H-R system can be controlled to reach arbitrary n-periodical (n = 1, 2, 3, 4, 5, 6,...) orbit or stable state even when just one variable is feed backed into the system intermittently. The chaotic Chua circuit is also investigated to check its model independence and effectiveness of the schemes and the equivalence of the two schemes are confirmed again. [ABSTRACT FROM AUTHOR]

This paper proposes a scheme of parameter perturbation to suppress the stable rotating spiral wave, meandering spiral wave and turbulence in the excitable media, which is described by the modified Fitzhugh-Nagumo (MFHN) model. The controllable parameter in the MFHN model is perturbed with a weak pulse and the pulse period is decided by the rotating period of the spiral wave approximatively. It is confirmed that the spiral wave and spiral turbulence can be suppressed greatly. Drift and instability of spiral wave can be observed in the numerical simulation tests before the whole media become homogeneous finally. [ABSTRACT FROM AUTHOR]

We investigate the noise-induced synchronization between two identical uncoupled Hodgkin-Huxley neurons with sinusoidal stimulations. The numerical results confirm that the value of critical noise intensity for synchronizing two systems is much less than the magnitude of mean size of the attractor in the original system, and the deterministic feature of the attractor in the original system remains unchanged. This finding is significantly different from the previous work [Phys. Rev. E 67 (2003) 027201] in which the value of the critical noise intensity for synchronizing two systems was found to be roughly equal to the magnitude of mean size of the attractor in the original system, and at this intensity, the noise swamps the qualitative structure of the attractor in the original deterministic systems to synchronize to their stochastic dynamics. Further investigation shows that the critical noise intensity for synchronizing two neurons induced by noise may be related to the structure of interspike intervals of the original systems. [ABSTRACT FROM AUTHOR]

The film properties and microstructures of (bottom)Si/SiO2/Ti(top) and (bottom)Si/SiO2/Ti/TiN/AlCu(top) stacks deposited by different processes were characterized. The resistivities of thin Ti films and the reflectivities of AlCu alloy films were found to correlate with the microstructure as well as the mean time to failure (MTTF) in the electromigration (EM) test. A quick-turn monitor for AlCu interconnect reliability in the semiconductor manufacturing industry was established. [ABSTRACT FROM AUTHOR]

We report the detection of diffuse halos (LAHs) around star-forming galaxies at z ∼ 5.7 by stacking 310 spectroscopically confirmed emitters (LAEs). The majority of the LAEs are identified from our spectroscopic survey of galaxies at z > 5.5. They are all located in well-studied fields with deep narrowband and broadband imaging data. We combine the LAE sample and its subsamples in the narrowband NB816 (i.e., the band) and z band (i.e., the continuum band). By comparing the stacked objects with their corresponding point-spread functions, we clearly detect extended LAHs around these LAEs. We perform sophisticated simulations and analyses on statistical and systematic errors, and confirm that the detected halos are not caused by errors. The scale lengths of the LAHs, when described by a double-component model, range from 1.2 to 5.3 kpc with a typical value of ∼2 kpc. The LAH sizes from our sample are in agreement with those of individual LAEs at the similar redshift measured by Very Large Telescope/MUSE but are relatively smaller than those of photometrically selected LAEs in previous studies. We also find that LAEs with higher luminosities, higher UV-continuum luminosities, or smaller equivalent widths tend to have larger LAH sizes. Our results are consistent with a scenario that LAHs originate from the scattered light of the central galaxies by H i gas in the circumgalactic medium. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) plays an integral role in the metabolism of liver and development of the skeleton in humans. To date, the interactions between different-duration terahertz (THz) radiation and ALP activities, as well as the influence mechanism are still unclear. In this study, using the para-nitro-phenyl-phosphate (pNPP) method, we detect changes in ALP activities during 40-minute THz radiation (0.1 THz, 13 mW/cm2). It is found that the activity of ALP decreases in the first 25 min, and subsequently increases in the later 15 min. Compared with the activity of ALP being heated, the results suggest that short-term terahertz radiation induces a decrease in enzyme activity through the non-thermal mechanism. In order to explore the non-thermal effects of THz radiation on ALP, we focus on the impacts of 0.1 THz radiation for 20 min on the activity of ALP in different concentrations. The results reveal that the activity of ALP decreases significantly after exposure to THz radiation. In addition, it could be deduced from fluorescence, ultraviolet-visible (UV-vis), and THz spectra results that THz radiation has induced changes in ALP structures. Our study unlocks non-thermal interactions between THz radiation and ALP, as well as suggests that THz spectroscopy is a promising technique to distinguish ALP structures. [ABSTRACT FROM AUTHOR]

Misfit strain is inevitable in various heterostructures like the graphene/MoS2 van der Waals heterostructure. Although the misfit strain effect on electronic and other physical properties have been well studied, it is still unclear how the misfit strain will affect the performance of the nanomechanical resonator based on the graphene/MoS2 heterostructure. By performing molecular dynamics simulations, we disclose a misfit strain-induced decoupling phenomenon between the graphene layer and the MoS2 layer during the resonant oscillation of the heterostructure. A direct relationship between the misfit strain and the decoupling mechanism is successfully established through the retraction force analysis. We further suggest to use the graphene/MoS2/graphene sandwich heterostructure for the nanomechanical resonator application, which is able to prevent the misfit strain-related decoupling phenomenon. These results provide valuable information for the future application of the graphene/MoS2 heterostructure in the nanomechanical resonator field. [ABSTRACT FROM AUTHOR]

Based on an InGaN/GaN light emitting diode (LED) structure, monolithically integrated vertical driving metal-oxide-semiconductor field-effect transistors (MOSFETs) were designed and experimentally implemented using a selective area growth (SAG) method. A simple p-GaN/n-GaN stack was selectively regrown on top of the LED wafer to realize an n/p/n structure for the vertical MOSFET fabrication. The integrated vertical MOSFET, which can effectively modulate the injection current through the serially connected LED, exhibited high performance such as an enhancement-mode (E-mode) operation with a relatively high output current density. However, on-resistance (RON) degradation was observed in the fabricated vertical MOSFET at a low drain bias level (VDS < 2 V). Through a 2D TCAD simulation, the origin of the high RON was revealed to be an electron barrier induced by the LED’s p-AlGaN electron blocking layer (EBL). The simulation results also demonstrated that it can be improved by band engineering of the EBL. [ABSTRACT FROM AUTHOR]

In recent years, the advances in terahertz applications have stimulated interest in the biological effects associated with this frequency range. We study the gene expression profile in three types of cells exposed to terahertz radiation, i.e., human ARPE-19 retinal pigment epithelial cells, simian virus 40-transformed human corneal epithelial cells, and human MIO-M1 Müller cells. We find that the gene expression in response to heat shock is unaffected, indicating that the minimum temperature increases under controlled environment. The transcriptome sequencing survey demonstrates that 6-hour irradiation with a broadband terahertz source results in specific change in gene expression and also the biological functions that are closely related to these genes. Our results imply that the effect of terahertz radiation on gene expression can last over 15 hours and depends on the type of cell. [ABSTRACT FROM AUTHOR]

We report initial results from a large Gemini program to observe z ≳ 5.7 quasars with GNIRS near-IR spectroscopy. Our sample includes 50 quasars with simultaneous ∼0.85–2.5 μm spectra covering the rest-frame ultraviolet and major broad emission lines from Lyα to Mg ii. We present spectral measurements for these quasars and compare with their lower redshift counterparts at z = 1.5–2.3. We find that when quasar luminosity is matched, there are no significant differences between the rest-UV spectra of z ≳ 5.7 quasars and the low-z comparison sample. High-z quasars have similar continuum and emission line properties and occupy the same region in the black hole mass and luminosity space as the comparison sample, accreting at an average Eddington ratio of ∼0.3. There is no evidence for super-Eddington accretion or hypermassive (>1010M⊙) black holes within our sample. We find a mild excess of quasars with weak C iv lines relative to the control sample. Our results, corroborating earlier studies but with better statistics, demonstrate that these high-z quasars are already mature systems of accreting supermassive black holes operating with the same physical mechanisms as those at lower redshifts. [ABSTRACT FROM AUTHOR]

Thermal properties of the diamond nanothread (DNT) forest array are studied using non-equilibrium molecular dynamics simulations. We find a strong anisotropic thermal property in this structure, i.e. the thermal conductivity in thread direction is over 300 times of that in the perpendicular direction. When subject to external strain, the thermal conductivity of the DNT forest decreases with increasing compressive/tensile strain in the thread direction, while thermal conductivity increases exponentially with increasing compressive strain in the perpendicular direction. The increase in thermal conductivity is attributed to the enhanced interactions among DNTs induced by compression. These results are explained by phonon spectra and structural deformation. Our findings show that diamond nanothread forest has a great potential application in the super-capacitors. [ABSTRACT FROM AUTHOR]

In micro air vehicles (MAVs), a magnetometer is usually employed for heading estimation. However, in real flight campaigns the magnetometer can easily suffer interference from external magnetic disturbances. In this paper, a simple novel method is proposed to conduct real-time calibration of the magnetometer subject to external disturbances with the aid of gravity and global navigation satellite system measurements. First, two equalities are derived from the rigid-body rotation equations. Then, the closed-form solution to the pseudo magnetometer biases is derived according to these equalities. To enhance the robustness of the solver, an optimizer based on a gradient-descent algorithm is proposed. The bifurcation analysis and convexity proofs are given to show that the proposed optimization has a unique solution and no local optimum. The execution time analysis of the proposed method also indicates that it is a very fast algorithm. Finally, the calibration parameters are determined by algebraic equations formed by pseudo biases. The proposed method is attitude-free, simple and easy-to-implement. The experiments on a real-world fixed-wing MAV demonstrate that the method is effective. [ABSTRACT FROM AUTHOR]

We report a facile process for fabricating flexible self-powered UV photodetectors with a planar metal–semiconductor–metal (MSM) structure. The device was assembled by transferring ZnO nanowires (NWs) onto two electrodes consisting of Ag NWs and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Ag NW film, both of which were formed by a simple self-assembly patterning method. The planar MSM heterostructure enables the device to generate photocurrents under zero bias voltage upon UV illumination. The smooth PEDOT:PSS/Ag NW film was found to be conducive to improving the device performance. Furthermore, the device was encapsulated in poly(dimethylsiloxane) (PDMS), ensuring a reliable performance under bending. [ABSTRACT FROM AUTHOR]

We perform both molecular dynamics simulations and theoretical analysis to study the sensitivity of the mass sensor based on graphene nanomechanical resonators, which are actuated following the global extended mode or the localized edge mode. We find that the mass detection sensitivity corresponding to the edge mode is about three times higher than that corresponding to the extended mode. Our analytic derivations reveal that the enhancement of the sensitivity originates from the reduction of the effective mass for the edge mode due to its localizing feature. Our findings shed light on improving the sensitivity of the graphene-based mass spectrometry by utilizing the localized edge mode. [ABSTRACT FROM AUTHOR]

We perform molecular dynamics simulations to investigate the energy dissipation of the resonant oscillation for the group IV monolayers of puckered configuration, in which the oscillation is driven with different actuation velocities. We find that, in the moderate actuation velocity regime, the nonlinear coupling between the resonant oscillation mode and other high-frequency modes will lead to the non-resonant motion of the system. For the larger actuation velocity, the effective strain generated during the resonant oscillating causes a structural transition from the puckered configuration into the planar configuration, which is a characteristic energy dissipation mechanism for the resonant oscillation of these group IV puckered monolayers. Our findings shed light on mechanical applications of the group IV monolayers in the nanomechanical resonator field. [ABSTRACT FROM AUTHOR]

We perform molecular dynamics simulations to investigate the irreversibility of crumpled graphene obtained by hydrostatic or biaxial compression. Our results show that there is a critical degree of crumpling, above which the crumpling is irreversible after the external force is removed. The critical degree of irreversible crumpling is closely related to the self-adhesion phenomenon of graphene, which leads to a step-like jump or decrease in the adhesion energy. We find the critical degree of crumpling is about 0.5 or 0.55 for hydrostatic or biaxial compression, which matches analytic predictions based on a competition between adhesive and bending energies in folded graphene. [ABSTRACT FROM AUTHOR]

Studies of the most luminous quasars at high redshift directly probe the evolution of the most massive black holes in the early universe and their connection to massive galaxy formation. However, extremely luminous quasars at high redshift are very rare objects. Only wide-area surveys have a chance to constrain their population. The Sloan Digital Sky Survey (SDSS) has so far provided the most widely adopted measurements of the quasar luminosity function at . However, a careful re-examination of the SDSS quasar sample revealed that the SDSS quasar selection is in fact missing a significant fraction of quasars at the brightest end. We identified the purely optical-color selection of SDSS, where quasars at these redshifts are strongly contaminated by late-type dwarfs, and the spectroscopic incompleteness of the SDSS footprint as the main reasons. Therefore, we designed the Extremely Luminous Quasar Survey (ELQS), based on a novel near-infrared JKW2 color cut using Wide-field Infrared Survey Explorer mission (WISE) AllWISE and 2MASS all-sky photometry, to yield high completeness for very bright () quasars in the redshift range of . It effectively uses random forest machine-learning algorithms on SDSS and WISE photometry for quasar–star classification and photometric redshift estimation. The ELQS will spectroscopically follow-up ∼230 new quasar candidates in an area of ∼12,000 deg2 in the SDSS footprint to obtain a well-defined and complete quasar sample for an accurate measurement of the bright-end quasar luminosity function (QLF) at . In this paper, we present the quasar selection algorithm and the quasar candidate catalog. [ABSTRACT FROM AUTHOR]

We present a spectroscopic survey of high-redshift, luminous galaxies over four square degrees on the sky, aiming to build a large and homogeneous sample of Lyα emitters (LAEs) at and 6.5, and Lyman-break galaxies (LBGs) at . The fields that we choose to observe are well studied, such as by the Subaru XMM-Newton Deep Survey and COSMOS. They have deep optical imaging data in a series of broad and narrow bands, allowing for the efficient selection of galaxy candidates. Spectroscopic observations are being carried out using the multi-object spectrograph M2FS on the Magellan Clay telescope. M2FS is efficient enough to identify high-redshift galaxies, owing to its 256 optical fibers deployed over a circular field of view in diameter. We have observed ∼2.5 square degrees. When the program is completed, we expect to identify more than 400 bright LAEs at and 6.5, and a substantial number of LBGs at . This unique sample will be used to study a variety of galaxy properties and to search for large protoclusters. Furthermore, the statistical properties of these galaxies will be used to probe cosmic reionization. We describe the motivation, program design, target selection, and M2FS observations. We also outline our science goals, and present a sample of the brightest LAEs at and 6.5. This sample contains 32 LAEs with Lyα luminosities higher than 1043 erg s−1. A few of them reach ≥3 × 1043 erg s−1, comparable to the two most luminous LAEs known at , “CR7” and “COLA1.” These LAEs provide ideal targets to study extreme galaxies in the distant universe. [ABSTRACT FROM AUTHOR]